Small-sized information equipment including a cellular phone and a Personal Digital Assistant (PDA) has become capable of connection to a network and storage of a large amount of personal information with recent sophistication of functions, and a demand for improvement of security function in such equipment is extremely high.
In order to ensure security in such equipment, personal identification using a password or ID (IDentifiacton) card, which has been widely used, may be employed. However, the password or ID card has a high risk of plagiarism, and realization of more reliable personal identification (identification that a user of equipment is the user himself/herself registered in advance) is in a strong demand. Personal identification by biometrics information is highly reliable and considered to be able to satisfy the above demand. Particularly, use of a fingerprint as the biometrics information is convenient.
When the fingerprint is used as the biometrics information for personal identification, a fingerprint (pattern consisting of ridge lines, which can contact with a sampling surface of a fingerprint sensor, and valley lines, which do not contact with the sampling surface) is sampled by a capacitance type fingerprint sensor or an optical fingerprint sensor from a finger of a person to be identified as image information. Then, by extracting characteristic information (position information on branch points and endpoints, for example) from a foreground of the fingerprint image (ridge line image, for example) and by verifying the extracted characteristic information with registered characteristic information of the person to be identified that was registered in advance, determination is made if the person to be identified is the person himself/herself, that is, personal identification is performed.
A general fingerprint sensor for sampling a fingerprint image from a person to be identified (hereinafter referred to as planar finger sensor in some cases) usually has a sensor surface (sampling surface) larger than the size of a finger. However, in order to mount a fingerprint sensor in small-sized information equipment such as a cellular phone and PDA, the size of the sensor surface is made smaller than that of a finger and a plurality of partial images continuously sampled through the sensor surface are integrated to obtain an image of the entire fingerprint.
Such a situation is handled by a sweep type fingerprint sensor. This sweep type fingerprint sensor has a rectangular sampling surface (sensor surface/image pickup surface) with the length sufficiently shorter than that of a finger and having a small area. Attempts are made such that, by moving a finger with respect to the sampling surface or by moving the sampling surface (fingerprint sensor) with respect to the finger, a plurality of partial images of a fingerprint of the finger is continuously sampled and the entire fingerprint image of the finger is reconfigured from the sampled plural partial images. Note that, the above relative movement of the finger with respect to the sampling surface is referred to as “Sweep”. Moreover, information of minutiae (branch points or end points of ridge lines) is extracted/generated from the reconfigured fingerprint image, and the above personal identification is performed based on the information.
In a personal identification system using a fingerprint as above, illegal use using a forged fingerprint has been pointed out as one of problems in realizing more reliable personal identification. That is, in the system using fingerprints, there is a possibility that a finger having a forged fingerprint is artificially made and impersonation might be committed using the artificial finger. And the illegal use by impersonation might undermine reliability of the system.
When silicon or rubber is used as a material for the artificial finger, since these materials do not conduct electricity and a capacitance type fingerprint sensor does not have a function to sample a fingerprint image from an artificial finger made of silicon or an artificial finger made of rubber, the above illegal use can not be committed. The optical fingerprint sensor can not sample a fingerprint image from an artificial finger made of silicon or an artificial finger made of rubber in principle, either.
However, it is pointed out that, if gummy substance (substance having the same water content as a human finger, obtained by gelatinizing a gelatin solution) with composition extremely close to that on a human skin is used as the material for the artificial finger, since the gummy substance conducts electricity, the capacitance type fingerprint sensor or optical fingerprint sensor can sample a fingerprint image from the artificial finger made of gummy substance, which enables illegal use by impersonation.
Then, the above-mentioned planar fingerprint sensor has employed a method to detect if a finger, for which a fingerprint image is being sampled, is a living body or not while the finger is placed on a sensor surface of the planar fingerprint sensor to prevent impersonation (illegal use using a forged fingerprint) by an artificial finger (forged fingerprint (See the following Patent Documents 1 to 8, for example).
Patent Document 1: Japanese Patent Laid-Open (Kokai) No. Sho 62-74173
Patent Document 2: Japanese Patent Laid-Open (Kokai) No. Hei 2-110780
Patent Document 3: Japanese Patent Laid-Open (Kokai) No. Hei 2-144684
Patent Document 4: Japanese Patent Laid-Open (Kokai) No. Hei 2-144685
Patent Document 5: Japanese Patent Laid-Open (Kokai) No. Hei 2-259969
Patent Document 6: Japanese Patent Laid-Open (Kokai) No. Hei 6-187430
Patent Document 7: Japanese Patent Laid-Open (Kokai) No. Hei 11-45338
Patent Document 8: Japanese Patent Laid-Open (Kokai) No. 2000-172833
On the other hand, with the above-mentioned sweep type fingerprint sensor, the finger should be moved with respect to the rectangular sampling surface in a strip state to sample a fingerprint image, and the sweep type fingerprint sensor can not detect if the finger, for which the fingerprint is to be sampled, is a living body or not with the methods disclosed in the above Patent Documents 1 to 8. A detection surface for detecting a living body may be provided in addition to the rectangular sampling surface so that fingerprint sampling and living-body detection can be performed separately. However, in this case, illegal use by impersonation is possible by using a real finger (living body) on the detection surface while using a forged fingerprint on the rectangular sampling surface. Therefore, reliable detection on whether the finger, for which a fingerprint image is just being sampled, on the rectangular sampling surface of the sweep type fingerprint sensor is a living body or not is in demand.
Moreover, personal identification using image information of iris, face, auricle or the like as biometrics information is known other than the personal identification using a fingerprint as biometrics information. In this case, a picture of an iris, face, auricle or the like is taken by a camera and characteristic information is extracted from the captured image, and the extracted characteristic information is verified with registered characteristic information of a person to be identified, which is registered in advance, so as to determine if the person to be identified is the person himself/herself, that is, to perform personal identification. However, even in this personal identification, illegal use by impersonation is possible by presenting a display device displaying a high-definition dynamic image or a still image or presenting a printed matter on which a high-definition image is printed out. Therefore, even in the case of personal identification using image information of iris, face, auricle or the like as biometrics information, reliable detection on whether the iris, face, auricle or the like being captured by a camera as biometrics information is a forged one such as a display or a printed matter is in demand.
The present invention was made in view of the problems stated above and has an object to surely preclude illegal use by impersonation using a forged fingerprint or the like and to realize more reliable personal identification by enabling reliable detection on whether a living body portion, for which a fingerprint image is being sampled, for example by a sweep type fingerprint sensor, is a living body or not, so that a non-living body such as an artificial finger made of gummy substance or the like and a living body can be surely discriminated.
Moreover, the present invention has an object to surely preclude illegal use by impersonation using a forged one or the like and to realize more reliable personal identification by enabling reliable detection on whether an iris, face, auricle or the like being captured by a camera, for example, as biometrics information is a forged one such as a display or a printed matter so that a forged one and a living body can be surely discriminated.